[chenicalper]

As it tells at the subject?
We have a solution of salt and water. We want to precipitate the salt. For increasing the rate of precipitation there is a method called as, ''scratching method'' . In this method you scratch the sides of the glass with a rod. And it is known that this increases the rate of precipitation.
How does it work? What is the mechanism? Are we disturbing the layer of thin precipitate at the sides of the glass, and creating new surfaces, or are we just making vibration and destroying the possible emulsions?
I ll be very pleasent if somebody can help me because tomorrow is the laboratory day and I am the teaching asistant in this lab I am sure many of these clever students will ask to me, as I ask to you
''How scratching method works?''

[mike]

Scratching forms a nucleation site from which a phase transformation can occur.

http://en.wikipedia.org/wiki/Nucleation

Good luck with the lab